This invention primarily relates to image converters and to cameras incorporating image converters operated in a framing mode. The invention may be applicable to cathode ray tubes other than image converters.
Methods of using image converter tubes, hereinafter called simply image converters, to produce, for example, a multiplicity of two dimensional images at high repetition rates are well known. In these methods, an electron beam is usually governed by two operations. The first comprises switching the beam on and off repetitively so as to provide, in effect, a shuttering action. The second is the deflection of the beam in such a way that the successive images appear at different parts of the screen of the tube. The present invention is primarily though not exclusively concerned with the second operation.
In order to deflect an electron beam in an image converter to successive stationary positions on the screen it is necessary according to the ordinary practice hitherto to generate a staircase waveform for application to a pair of electrostatic deflector plates. As is described by A. E. Huston and S. Majumdar in "The Imacon--a new image converter camera " Proceedings of the Eighth International Congress on high speed photography, pages 25 and 26 (Stockholm 1968) a sinusoidal oscillation was used to provide repetitive shuttering by deflection of the electron beam across an aperture. The beam was deflected to give two vertically separated positions and circuits using thermionic valves were used to generate a staircase waveform to give horizontal deflection to discrete positions on the tube screen. Such a technique provides a framing camera with a multiplicity of image positions in two rows. The amplitude of each step of a staircase must be of the order of at least 400 volts and in practice a multiplicity of steps are necessary. The control and timing of the application of potentials to the deflector plate must be performed by circuits which can accommodate potentials of several thousand volts. This necessity is rather inconvenient and in particular is not easily made compatible with the use of solid state devices in such circuits.